In a welcome move earlier today, Valve made its position clear regarding the use of Steam's in-game item trading functionality, and its use by CS:GO weapon skin gambling sites. Basically, the company confirmed that it's not permitted, writing that the use of "the OpenID API and making the same web calls as Steam users to run a gambling business is not allowed by our API nor our user agreements."
Valve wrote that it intends to send requests to gambling sites to cease their operations, and if they don't, Valve will "pursue the matter as necessary". Following that statement, Twitch has made one of its own, and while it's not necessarily a new update to its terms of service, it makes explicit that streaming gambling activities of this nature is not allowed – at least in cases where the gambling runs contrary to the third-party's TOS, such as it does with Steam.
"As such, content in which the broadcaster uses or promotes services that violate Valve’s stated restrictions is prohibited on Twitch. Our Rules of Conduct lists other examples such as playing pirated games and playing on unauthorized private servers."
These statements follow revelations last week that two popular CS:GO streamers had not disclosed their co-ownership of CSGO Lotto, despite producing videos using the gambling site. That has prompted closer scrutiny of the skin gambling scene as a whole.